1) Field of the Invention
The present invention relates to a cleaning unit for cleaning of a rotator such as a photosensitive drum or a paper carrying belt, a process cartridge equipped with the cleaning unit, an image forming apparatus, and a toner used in the image forming apparatus.
2) Description of the Related Art
Color image forming apparatus that use electrophotography have been widely used in recent years. With easy availability of digitized image, more and more highly accurate printed image is demanded. While high resolution and gradation are being studied, as improvement in toner that visualizes latent image, the reduction of particle size and spherical particle size making of toner are being studied to form a highly accurate image.
For example, the following four methods of obtaining toner are proposed. In the first method, toner with spherical particle size and with specific particle size distribution is obtained by milling, as disclosed in Japanese Patent Application Laid Open Publications No. Hei1-112253, No. Hei2-284158, No. Hei3-181952, and No. Hei4-162048. In the second method, toner with small spherical particles is obtained by suspension polymerization, as disclosed in Japanese Patent Application Laid Open Publication No. Hei5-72808. In the third method, toner with small spherical particles is obtained by mixing a binder resin and a colorant in nonaqueous solvents and dispersing this mixture in an aqueous medium in the presence of a dispersion stabilizer, as disclosed in Japanese Patent Application Laid Open Publication No. Hei9-15902. In the fourth method, toner with small spherical particles is obtained by mixing a binder resin partially modified and a colorant in organic solvents, dispersing the mixture in an aqueous medium, and allowing to undergo polyaddition reaction of the modified resin, as disclosed in Japanese Patent Application Laid Open Publication No. Hei11-133668. Use of such toner improves image quality and fluidity of toner.
However, there are some problems with toner with small spherical particles. For example, during cleaning of toner not transferred and remained on a photosensitive drum using a cleaning blade, the spherical toner particles rotate between the blade and the photosensitive drum and enter the gap between the two, thereby making the cleaning difficult. To avoid this problem, a method of preparing toner with small random shaped particles is proposed in Japanese Patent Application Laid Open Publication No. Hei5-188642. In this method, a polymer obtained by suspension polymerization is heated in a dispersing medium beyond glass transition point to obtain an agglomerate. The agglomerate is introduced in a jet stream warmed up. Then the agglomerate is cracked and dried simultaneously to obtain the desired toner particles. Moreover, a method of preparing toner particles with rugged surface is proposed in Japanese Patent Application Laid Open Publication No. Hei9-15903. In this method, a binder resin and a colorant are mixed in nonaqueous solvents. This mixture is dispersed in an aqueous medium in the presence of a dispersion stabilizer and thereby suspension is obtained. The solvents and medium are removed from the suspension, by at least one of heating and pressure reduction to obtain the desired toner particles.
Moreover, wax and inorganic fine particles that are added internally or externally to improve mold releasing characteristics and fluidity respectively, are separated from the toner, and adhered on the photosensitive drum. This is another problem. Smaller is the particle size, more is the proportion of additives like wax, inorganic fine particles etc. Thus, there is a tendency towards increase in particles that adhere on the photosensitive drum.
A cleaning unit that includes a cleaning blade and a cleaning roller with an abrasive coated on the surface is proposed in Japanese Patent Application Laid Open Publication No. Hei10-111629, as a measure to remove the particles adhered to the photosensitive drum. However, the abrasive coated on the surface of the cleaning roller tend to come off and it is difficult to maintain good cleaning over a long period of time. Furthermore, in Japanese Patent Application Laid Open Publication No. 2001-296781, a structure to remove the particles adhered on the photosensitive drum in which an abrasive is stuck to the tip of the cleaning blade of the cleaning unit is proposed. However, it is difficult to clean the toner remaining after transferring of image and remove substance adhered to the surface simultaneously. In this structure with an abrasive stuck on the tip of the cleaning blade, the abrasive tend to come off.
However, with the conventional cleaning blade or the cleaning unit having a cleaning blade, it is difficult to remove sufficiently the substance adhered on the photosensitive drum. If the substance adhered contains wax as a main component, there is a thin filming on the surface of the photosensitive drum. If the substance adhered contains organic fine particles as a main component, these particles act as a core and grow bigger by up taking of additives like calcium carbonate etc. that are included in a recording paper, thereby deteriorating the image more and more as the time elapses. The contamination of an intermediate transferring body on which a toner image is transferred from the photosensitive drum and carried, is similar to that of the paper carrying belt that supports and carries a recording paper to which the toner image is transferred. Therefore, a cleaning unit that cleans surfaces of these components sufficiently is desired.